Re: Scheduling behaviour issue

[Simon Wright <simon@pushface.org>]

fabien.chouteau@gmail.com writes:

> On Wednesday, April 22, 2020 at 1:34:53 PM UTC+2, Simon Wright wrote:
>> but FreeRTOS adds the preempted task at the *tail* of its ready queue
>> ([4], section Prioritized Pre-emptive Scheduling (without Time Slicing),
>> on page 95 or thereabouts).
>
> I couldn't find the paragraph that says that.

It's the dicussion after Figure 29.

There are 2 "continuous" tasks (no interaction with the scheduler) of
the same priority, say A & B (this is so unlike any real-time system
I've encountered! You might have just one, doing some sort of
housekeeping or monitoring).

Both A and B are ready. One of the tasks, A, runs until a
higher-priority task C preempts it; when the higher-priority task
finishes, *the other task* B runs!

> That seems very strange to not resume the task that was just
> preempted.

I so agree. I think it's because the mechanism used is derived from
FreeRTOS's round-robin scheduler.